The present invention relates to an FRAM utilizing non-volatility, as an infrared ray sensor utilizing the pyroelectric effect, a memory element and a ferroelectric element widely used as a communications part, a memory cell thereof, and a method of producing the same.
A non-volatile semiconductor memory, such as a ROM (read-only memory), which is able to hold stored data even when the power source is turned off, has an inherent problem in that a limitation is imposed on the number of times data and the speed is low. On the other hand, a RAM (random access memory) features a high data rewriting speed. In particular, an FRAM which uses a ferroelectric material exhibits very excellent non-volatility as well as the ability to rewrite data a great number of times, such as 1010 to 1012 times, owing to the use of two residual polarizations of different polarities. Besides, the rewriting speed is as fast as a value in the order of .mu.s or shorter, and so this memory is drawing attention as an ideal memory of the next generation.
Efforts have been made to develop a FRAM having a large capacity, featuring non-volatility and operating at high speeds. However, the affinity to wear of the film is a serious problem in that the spontaneous polarization (Pr) of the ferroelectric material decreases with an increase in the number of times of writing. It has been known that the capacity can be increased and the durability can be improved (1) by employing a ferroelectric material having a large spontaneous polarization (Pr), and (2) by employing a ferroelectric material which is immune to wear. Oxides of the perovskite structure have been widely used as such materials. Among them, it has been known that PZT (Pb(Zr.sub.1-x Ti.sub.x)O.sub.3) which is a single lattice having a crystal structure which is the perovskite structure, exhibits a large Pr without crystalline anisotropy. A diode made of this material which is used as a non-volatile memory has been disclosed in International Electron Device Meeting Technical Digest 1989, p. 255 (IEEE IEDM Tech. Dig.: 255-256, 1989). There has further been known SrBi2Ta2O9 of a Bi laminar ferroelectric material having a crystalline structure in which a plurality of single lattices of the perovskite structure are overlapped one upon the other. In this material, Pr exhibits a crystalline anisotropy only in a direction perpendicular to the c-axis. Though the Pr value is not so large, the material exhibits an excellent resistance to wear. Examples of using this material have been disclosed in Patents WO93/12542 and PCT/US92/10627.